The present invention relates generally to a vehicle navigation system that has the capability to determine in real time the position of the vehicle relative to data contained in a database that represents the road network on which the vehicle is traveling. The present invention more particularly relates to programs and methods that improve vehicle positioning accuracy when using differential wheel sensors with a vehicle navigation system.
In-vehicle navigation systems provide a variety of useful features to end users (i.e., the drivers and/or passengers of the vehicles in which the navigation systems are installed). Included among the features that are provided by some in-vehicle navigation systems are route calculation, route guidance, emergency roadside services, electronic yellow pages, and so on. In order to provide these kinds of features, in-vehicle navigation systems use geographic data. The geographic data include information about features in a covered geographic region. The geographic data include information about the location of roads, the speed limits along roads, turn restrictions at intersections, the names of roads, the address ranges along roads, the locations of points of interest, and so on.
Some of the features provided by in-vehicle navigation systems require that the position of the vehicle be determined. There are several considerations related to determining the position of the vehicle. For example, a GPS (Global Positioning System) may be used to obtain the geographic coordinates of the vehicle. However, the geographic coordinates only indicate the position of the vehicle relative to the surface of the earth. For some of the features provided by in-vehicle navigation systems, a means is required to determine the vehicle position relative to the road network on which the vehicle is traveling and the direction of the vehicle along the road segment. In order to determine the position and heading of a vehicle along a road segment, a vehicle navigation system uses a geographic database and one or more sensors in addition to the GPS system.
One type of sensor that can be used in a vehicle navigation system to determine the vehicle position or heading is a differential wheel speed sensor. A differential wheel speed sensor can be used to determine changes in vehicle heading by comparing the distances traveled by a left and right wheel of the vehicle. Once the vehicle position is determined relative to the road segment represented by the geographic database, programming in the in-vehicle navigation system can be used to provide various features, such as determining a route to a desired destination, providing maneuvering instructions for reaching the destination, identifying the closest restaurant or gas station relative to the vehicle position, displaying a map of the area around the vehicle, and so on.
An advantage associated with using differential wheel speed sensors in navigation systems is that they are relatively inexpensive. Although differential wheel speed sensors are relatively accurate, there is room for improvement. Accordingly, it is an objective to improve the accuracy of vehicle heading determinations when using differential wheel speed sensors.
To provide improvements over the prior art, a vehicle positioning application is disclosed that includes a means for a differential wheel speed (DWS) heading change determination (hereinafter sometimes referred to as xe2x80x9cDWS headingxe2x80x9d) and means for correcting the DWS heading determination to account for changes in wheel radii. The DWS heading may then be used to correct the vehicle heading determination in certain embodiments.
Each of the various corrective aspects according to the exemplary embodiments of the present invention may be instituted as various software, firmware, or other processing routines in any desirable processor of the vehicle or its navigation system components utilizing the data gathered from a DWS sensor system as set forth herein or otherwise modified according to accepted techniques in the art.